All engines—diesel, gasoline, propane, and natural gas—produce exhaust gas containing carbon monoxide, hydrocarbons, and nitrogen oxides. These emissions are the result of incomplete combustion. Diesel engines also produce particulate matter. As more government focus is being placed on health and environmental issues, agencies around the world are enacting more stringent emissions' laws.
Because so many diesel engines are used in trucks, the U.S. Environmental Protection Agency and its counterparts in Europe and Japan first focused on setting emissions regulations for the on-road market. While the worldwide regulation of nonroad diesel engines came later, the pace of cleanup and rate of improvement has been more aggressive for nonroad engines than for on-road engines.
Manufacturers of nonroad diesel engines are expected to meet set emissions regulations. For example, Tier 3/Stage III A emissions regulations required an approximate 65 percent reduction in particulate matter (PM) and a 60 percent reduction in NOx from 1996 levels. As a further example, Interim tier 4/Stage III B regulations required a 90 percent reduction in PM along with a 50 percent drop in NOx. Still further, Final Tier 4/Stage IV regulations, which will be fully implemented by 2015, will take PM and NOx emissions to near-zero levels.
In known SCR systems, an undispensed portion of a reductant is disseminated to the reductant tank. The undispensed portion of the reductant may flow in an undistributed, smooth stream into the reductant that is already being held in the reductant tank. If the reductant in the reductant tank is frozen, then the undispensed portion of the reductant, being in a relatively warmer, liquid form, initially creates a small hole in the frozen reductant. Eventually, the small hole enlarges such that the undispensed portion of the reductant flows right through the hole to the bottom of the reductant tank. During these conditions, the SCR system does not effectively leverage the warming capacity of the undispensed portion of the reductant.
Further, in known SCR systems, the undispensed portion of the reductant is not aimed towards any specific component in the reductant tank, such as a level sensor, thereby potentially leaving the level sensor frozen in place for longer than necessary.